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ISHS Acta Horticulturae 1134: VIII International Symposium on Light in Horticulture

Timing of blue and red light exposure and CPPU application during the raising of seedlings can control flowering timing of petunia

Authors:   N. Fukuda, H. Oba, D. Mizuta, H. Yoshida, J.E. Olsen
Keywords:   cytokinin, floral induction, LED, light quality, shoot elongation, morphogenesis
DOI:   10.17660/ActaHortic.2016.1134.23
As previously shown, blue (B) light promotes shoot elongation and flowering in petunia, whereas red (R) light inhibits these responses. Here we aimed to test whether the plant growth regulator CPPU and temporal B light irradiation could induce floral bud initiation while still keeping the dwarfed plant shape observed under R light. In this respect, we evaluated effects of irradiation timing of B and R light, and CPPU application during raising of seedlings on subsequent growth and floral induction in petunia (Petunia hybrida 'Baccarat blue' and 'Merlin blue Moon'). Petunia plants were grown under white fluorescent light (WFL) until seven true leaves had developed. They were then exposed to WFL, R and B light from LEDs in growth cabinets with a 14-h photoperiod for 4 weeks. In one experiment, 0, 1 or 10 ppm CPPU was applied to plants during R treatment for 4 weeks before being moved into a greenhouse. The treatment with 10 ppm CPPU induced flowering 4 to 7 days earlier compared to the exposure to R only with keeping the dwarfed plant shape. In another experiment, plants were exposed to R and B for different periods; plants were either continuously grown under R LED or exposed to B LED during the last 1, 2 or 3 weeks during raising of the seedlings. After these treatments, plants were moved into a greenhouse. Longer duration of exposure to B LED induced earlier flowering. After 3 weeks exposure to B LED, 'Baccarat blue' and 'Merlin blue' flowered earlier as compared to continuous exposure to R LED, but there was no difference in plant height among treatments. In conclusion, R light and CPPU treatment during raising of seedlings, could be used to control plant morphology and timing of flowering in petunia.

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